The report also says the frequency of sectarian bloodletting means bodies are often found which "bear signs indicating that the victims have been brutally tortured before their extra-judicial execution".

It concludes that torture threatens "the very fabric of the country" as victims exact their own revenge and fuel further violence.

Mr Nowak said he would like to visit Iraq in person, but the current situation would not allow him to prepare an accurate report, because it would not be safe to leave Baghdad's heavily guarded Green Zone where the Iraqi government and US leadership are situated.